Fault Confinement Mechanisms on CAN : Analysis and Improvements

International audienceThe CAN protocol possesses fault confinement mechanisms aimed at differentiating between short disturbances caused by electromagnetic interferences (EMI) and permanent failures due to hardware dysfunctioning. In this study, we derive a Markovian analysis of these mechanisms which enable to assess the risk of reaching one of the two degraded modes bus-off and error-passive defined by CAN. We identify several problems with the existing mechanisms, the major one being that the busoff state is reached too easily. In particular it happens with bursts of EMI causing several consecutive transmission errors. We propose new mechanisms that address these drawbacks. The basic idea is to weigh the progression towards the degraded mode by the quantity of information given by the last transmission. In our experiments, these mechanisms proved to be effective: the hitting time of bus-off for non-faulty nodes increases hugely while faulty systems reach bus-off in the same amount of time. In the last part of the paper, implementation issues are discussed and different techniques for tuning the parameters of the algorithm are provided, either off-line or at run-time